This invention relates to direct current (DC) power converters for electronic watches and more particularly to a power converter employing capacitors arranged in circuit to develop high operating potentials from a low potential source.
The power converter, generally, functions to provide a high output potential from a lower potential source such as a battery.
An example of a typical use of such a converter is in an electronic timepiece or electronic watch. Such devices are relatively new and essentially are completely electronic time-keeping devices fabricated with integrated circuits and associated displays. Such watches are ultra-miniature and provide the user with extremely accurate time indication in a wrist watch configuration. As such, the watches are energized by means of small batteries which typically provide an output voltage of about 1.5 volts. This voltage, while capable of operating and biasing certain types of integrated circuits, is usually much too low to operate the display circuits associated with such watches. For example, a low power, reliable display employs the liquid crystal. Such displays require larger operating potentials than that supplied by the battery.
The system employed in such watches utilizes a relatively high frequency crystal oscillator. The oscillator utilizing a quartz resonator is extremely stable and provides an accurate output frequency. This frequency is conventionally divided down by means of multivibrator or other types of digital counting circuits, to produce, for example, a 1 Hz signal analagous to a 1 second time interval. In turn, this signal is counted by multiples of 60 for minute indication. The minute counter provides a reference to indicate the 60 minute per hour count and hence hours. The watch circuitry displays the contents of the second, minute and hour digital counters to provide signals for energizing a digital time display. Such counters may interface with the display, by means of gating circuits as AND gates and so on to indicate the time of day in a direct reading digital format. In conjunction with the fact that displays as liquid crystals, light emitting diodes and so on operate at higher potential levels that that supplied by the battery, it is also desireable in many instances to operate the logic circuitry at higher potentials (greater than 1.5 volts) to achieve greater immunity to noise and, hence, more reliable operation in general.
Thus, to obtain such potential levels, one utilizes a power converter to raise the battery potential to a desired value.
Many techniques for doing so exist in the prior art. Certain techniques employ the use of inductors which due to their response to current changes, can provide high voltage spikes or transients, which are then rectified and filtered to produce higher potential output levels. Inductors tend to be bulky and difficult to fabricate in ultra-miniature size so as to be compatible with the requirements of the electronic watch. Inductors also produce magnetic fields and the associated transients can adversely affect the operation of the digital timekeeping circuitry employed in such a watch, as the counters, dividers, and so on.
Another commonly employed technique uses a transformer to provide a voltage step-up at a secondary winding. The primary of the transformer is supplied with an AC frequency at a given level usually derived from an oscillator or a switching circuit. The turns ratio of such transformers is such that a higher potential signal is produced at the secondary which signal is then rectified and filtered to produce the required higher level DC. These circuis present similar problems to the inductor converters in that the transformers are also bulky, the transients produce noise interference and the output is difficult to regulate because of circuit component tolerance.
However, there are a variety of circuit configurations which employ capacitors to effectuate potential conversion.
Such circuits are typically classified as voltage multipliers and basically operate as the above-described generic power converter. Basically, these circuits include doublers, triplers, or quadruplers and use capacitors to avoid the use of inductors or transformers. The circuits operate to transfer charge through diodes to provide higher operating DC potentials from a lower DC source. Examples of such circuits as well as certain of the above described converters can be had by reference to a text entitled "Radio Engineering Handbook" by Keith Henney, Fifth Edition, Chapter 17, pages 17-24, 17-25 and 17-26, a McGraw-Hill publication (1959).
As can then be verified, may typical prior art capacitor converters rely on charge transfer via diode circuits and depend upon voltage developed across the capacitors to afford charge transfers by the forward and reverse biasing of the diode.
The magnitude of the available outputs of such circuits are limited as well as the fact that an increase in the multiplication factors is associated with a reduction in efficiency of power. Hence, a quadrupler is less efficient and dissipates more power than a doubler and so on.
It is therefore an object of the present invention to provide efficient converters employing ultra-miniature capacitor elements under control of digital circuitry to develop high operating potentials at increased efficiency from a lower power source.
The converters employed are particularly suitable for use in electronic timepieces although other uses are obvious and apparent.